Vacuum Pump and Vacuum Systems Safety Manual

Vacuum Pump and Vacuum SystemsSAFETY MANUAL

P40040100_E Original instructions

edwardsvacuum.com

Copyright notice©Edwards Limited 2019. All rights reserved.

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Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Scope of this publication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Explosion risks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

When hazards arise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Operation / Commissioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Maintenance / Decommissioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Chemical sources of hazards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Chemical reactions and explosions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Homogeneous reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Heterogeneous reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Problems with abnormal reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Explosion hazards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Oxidants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Flammable / Explosive materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Pyrophoric materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Sodium azide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Toxic or corrosive materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Toxic materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Corrosive materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Summary - chemical sources of hazards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Physical sources of hazards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Types of over-pressure hazard. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Over-pressurised pump exhaust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Protection against exhaust over-pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Inlet over-pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Compressed gas supplies and back pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . 16Incorrect pump operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Summary - physical sources of hazards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Hazard analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

System design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Pressure ratings in a system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Elimination of stagnant volumes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Exhaust extraction systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Sources of potentially explosive gas or vapour mixtures. . . . . . . . . . . . . . . . . . . . . . . 20

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P40040100_E - Contents

Avoiding the flammable zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Levels of system integrity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Use of flame arrester protection systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Sources of ignition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Summary - system design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

The correct choice of equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Oil-sealed rotary vane and piston pumps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Edwards dry pumps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Pipeline design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Bellows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Flexible pipelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Anchor points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Seals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Physical over-pressure protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Pressure relief. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Over pressure alarm/trip. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Pressure regulators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Flame arresters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Purge systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Summary - the correct choice of equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Operating procedures and training. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Edwards Ltd, disclaim any and all liability and any warranty whatsoever relating to theaccuracy, practice, safety and results of the information, procedures or their applicationsdescribed herein. Edwards Ltd does not accept any liability for any loss or damage arising asa result of any reliance placed on the information contained in this presentation or theinformation provided being incorrect or incomplete in any respect. Note that theinformation contained herein is only advisory and, while Edwards can provide guidance withrespect to the potential hazards of using hazardous materials, it is the end-user’sresponsibility to conduct a risk assessment/hazard analysis specific to their operations andenvironment and to comply with government regulations.

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P40040100_E - Contents

Introduction

Scope of this publication

This document contains safety information associated with the specification, design,operation and maintenance of vacuum pumps and vacuum systems.

The document identifies some of the potential hazards which can arise and providesguidelines intended to help minimize the probability of safety hazards and to ensure that, ifa hazard arises, it is suitably dealt with.

This document is intended to be read by anyone who specifies, designs, installs, operates ormaintains vacuum pumps and vacuum systems. We recommend that this is read inconjunction with:

▪ The Instruction Manuals supplied with your equipment▪ Information provided by the suppliers of your process gases and chemicals▪ Information supplied by your safety department.

WARNING:Failure to obey the safety instructions given in this manual and the relevant pumpinstruction manual can cause serious harm or death.

If you require any further information on the suitability of Edwards products for your processapplication, or on safety aspects of your vacuum pumps or vacuum systems, please contactyour supplier or Edwards.

Explosion risks

Note:

Edwards pumps are available that meet the European ATEX directive for equipment used inpotentially explosive atmospheres.

Unexpected explosions are invariably caused by deviation from safety guidelines.Nevertheless, some of the incidents of explosions have been extremely violent and couldhave caused serious injury or death.

Common causes of violent rupture of a vacuum system component are ignition of flammablematerials, or the blockage or restriction of the pump exhaust. To avoid hazards, you shouldpay attention to the following to help ensure the safe operation of your vacuum pumps andsystems.

▪ Unless your system has been designed for pumping material at concentrationswhere it could be ignited in the vacuum pump, you must ensure that mixtures offlammables and oxidants are kept outside the flammable range. The use of inertpurge is one way of achieving this. See Avoiding the flammable zone on page 21.

▪ Ensure that exhaust blockages cannot occur during operation, either because ofmechanical components (for example, valves or blanks) or because of processmaterials or by-products depositing in pipelines, filters, and other exhaustcomponents, unless your system has been designed to cope with it.

▪ Use only PFPE (perfluoropolyether) oils in places of the pump mechanisms whichare exposed to high concentrations of oxygen or other oxidants. Other types of oils

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P40040100_E - Introduction

sold as "non-flammable" may only be suitable for use with concentrations ofoxidants up to 30 % v/v.

▪ Ensure that the accidental over pressure of a deliberately closed and isolatedvacuum system cannot occur; for example, as a result of a fault in a pressureregulator or purge control system.

▪ Where the pumped product can react violently with water, it is recommended thata cooling material other than water (for example, heat transfer fluid) be used inthe cooling circuit. Please consult Edwards for advice.

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P40040100_E - Introduction

When hazards ariseHazards can arise during all phases of a system's life. These phases are:

▪ Design▪ Construction▪ Operation / Commissioning▪ Maintenance / Decommissioning.

The types of problem which arise in each phase are summarized below. In all cases, youmust be aware that you can minimize the hazards in your system only when you have athorough understanding of the equipment and process / application in the system. If you arein doubt, you must ask your suppliers for more information or advice.

Design

When you design your system, you must choose the correct type of equipment for yourapplication. You must consider:

▪ the technical specification of the equipment▪ the materials used in the construction of the equipment▪ the operating consumables used with the equipment (such as lubricants and

operating fluids)▪ the process conditions and materials.

You must also think about the general suitability of the equipment for your application andensure that it will always be used within its specified operating conditions.

You must establish design procedures to ensure that errors in the design are reduced to aminimum. Such procedures should include an independent check of design calculations, aswell as consultation on design parameters.

Hazard analysis must always form part of your design review. You can eliminate manypotential hazards by careful consideration of the use of equipment in your system.

Construction

Reduce the probability of the occurrence of a hazard during construction by the use ofskilled and qualified personnel and quality assurance procedures. Skilled personnel are ableto identify the correct components that are required during assembly and are also able toidentify faulty or poorly manufactured components and equipment. Quality assuranceprocedures will help to identify and rectify poor workmanship and will ensure that thedesign specification is strictly followed.

Personnel must take special care and observe all safety precautions when installing newequipment in a system in which toxic, corrosive, flammable, asphyxiant, pyrophorics or otherhazardous substances have been pumped, produced or may still be present.

Electrical equipment must be installed by skilled / qualified personnel, in accordance with allappropriate local and national electrical regulations.

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P40040100_E - When hazards arise

Operation / Commissioning

Hazards can be caused during operation by equipment and component failure as a result ofage, improper use or poor maintenance. Reduce the probability of such hazards by propertraining in the use (and maintenance) of the equipment. Where necessary, refer to theinformation supplied by Edwards and your other suppliers in the form of InstructionManuals, training and after sales service.

Maintenance / Decommissioning

To prevent personnel coming into contact with dangerous substances, special care must beexercised and all safety precautions must be observed during maintenance of a system inwhich toxic, corrosive, flammable, pyrophoric, asphyxiants or any other substances havebeen pumped or produced.

Consideration should also be given to a planned maintenance program, and to the safedisposal of components which may be contaminated with dangerous substances. You mustfollow the maintenance advice given in the instruction manuals for all equipment to ensuresafe and reliable operation. Typically ATEX systems have additional requirements.

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P40040100_E - When hazards arise

Chemical sources of hazards

Chemical reactions and explosions

You must carefully consider all possible chemical reactions which in normal use, misuse andfailure conditions may occur at any point within your vacuum system. In particular, you mustcarefully consider reactions which involve gases and vapours which can lead to explosions.Experience has shown that explosions have occurred in which there were materials involvedwhich were not originally considered by the system designer, and in which the failure modeof such equipment had not been taken into account.

Homogeneous reactions

Homogeneous reactions occur in the gas phase between two or more types of gasmolecules. Gas combustion reactions are usually of this form. For example, to ourknowledge, the reaction between Silane (SiH4) and oxygen (O2) is always homogeneous.Therefore, if you have such reactions in a manufacturing process, you must carefully controlthe process pressure and reactant concentrations to prevent the occurrence of excessivereaction rates.

Heterogeneous reactions

Heterogeneous reactions require a solid surface to occur i.e. some gas molecules only reactwhen they are adsorbed onto a surface, but do not react in the gas phase at low pressures.This type of reaction is ideal for certain processes since it minimizes the effects of reactionswhich occur within the process chamber, reduces the generation of particulate, and reducesthe probability of contamination.

Most heterogeneous reactions become homogeneous at higher pressures, commonly wellbelow atmospheric pressure. This means that the way the gases react in process chamberswill not necessarily relate to the way that they react when compressed by a vacuum pump.

Problems with abnormal reactions

Abnormal reactions can occur when chemicals come into contact with gases or materialsthat the system designer has not anticipated. This can occur, for example, when there is aleak which allows either atmospheric gases to leak into the system, or toxic, flammable,explosive or other hazardous gases to leak out into the atmosphere.

To prevent the occurrence of these reactions, you should maintain a leak tightness of 1 x10-3 mbar l s-1 (1 x 10-1 Pa l s-1), or lower, in your system. High vacuum applications wouldtypically maintain a leak tightness of 1 x 10-5 mbar l s-1 (1 x 10-3 Pa l s-1) or lower. You mustalso ensure that all valves in the system are leak tight across their seats.

Gases which do not normally come into contact with each other during the process cyclemay be mixed in the pumping system and exhaust pipelines.

It is possible that water vapour or cleaning solutions may be present in the process chamberafter routine maintenance procedures. This could occur after the process chamber has beenflushed and cleaned. Water vapour may also enter the system from exhaust ducts andexhaust scrubbers.

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P40040100_E - Chemical sources of hazards

Where solvents are used to flush process deposits from the vacuum system, it is importantto ensure that the selected solvent is compatible with all the process materials in thevacuum system.

Explosion hazards

The source of explosion hazards generally falls into one of the following categories:

▪ Oxidants▪ Flammable / Explosive materials▪ Pyrophoric materials▪ Sodium azide.

Note that, in European Union (and some other) countries, suppliers of process materials arerequired by law to publish physical and chemical data for materials which they sell (usually inthe form of Material Safety Data Sheets). The data for a material must include, whereapplicable, information about the upper and lower explosive limits, the physical andthermodynamic properties of the material, and any health hazards associated with the useof the material. Refer to this information for guidance.

Oxidants

Oxidants such as oxygen (O2), ozone (O3), fluorine (F2), nitrogen trifluoride (NF3) andtungsten hexafluoride (WF6) are often pumped in vacuum systems. Oxidants react readilywith a wide range of substances and materials and the reaction often produces heat and anincreased gas pressure. The potential resultant hazards include fire and over-pressure in thepump and / or exhaust system.

To pump these gases safely, you must follow the gas supplier's safety instructions, togetherwith the following recommendations:

▪ Always use a PFPE (perfluoropolyether) lubricant in pumps which are used topump oxygen in concentrations above 25 % by volume in an inert gas.

▪ Use PFPE lubricants in pumps which are used to pump gases in which thepercentage of oxygen is normally below 25 % by volume, but which could rise toabove 25 % under fault conditions - if other oxidants other than oxygen arepumped, please consult the lubricant supplier for recommended levels of theoxidant present.

▪ PFPE lubricants are the preferred lubricants, but hydrocarbon type lubricants canbe used if a suitable inert gas purge is used to guarantee that the oil is not exposedto unsafe levels of the oxidant.

Under normal circumstances, PFPE lubricants will not oxidise or break down in an oil-sealedrotary vane or piston pump oil box or gear box and so this reduces the probability of anexplosion.

Note that thermal decomposition of PFPE lubricants may occur at or above a temperature of290 °C in the presence of air and ferrous metals. However, the thermal decompositiontemperature is lowered to 260 °C when titanium, magnesium, aluminium or their alloys arepresent.

If you do not want to use PFPE lubricants in oil-sealed rotary vane or piston vacuum pumps,you may dilute the oxidant to a safe concentration with an inert gas such as dry nitrogen.This approach is only feasible for low flow rates of oxidant gases. You must install safetyfeatures in your system to ensure that the minimum flow of the inert dilution gas required toreduce the concentration of the oxidant to a safe level is always available, and to ensure that

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the flow of oxidant does not exceed the maximum allowed flow rate. You must design yoursystem so that the flow of oxidant stops immediately if these conditions are not met.

We recommend that you use Edwards dry pumps when you pump oxidants (see Section7.2Edwards dry pump Edwards dry pumps on page 28). Dry pumps have no sealing fluids inthe swept volume and so there is a greatly reduced probability of the occurrence of anexplosion if you use a dry pump to process oxidants. Edwards recommends an inert gaspurge for the bearings and into the gear box when a hydrocarbon lubricant is used.

Flammable / Explosive materials

Many gases and dusts, such as hydrogen (H2), acetylene (C2H2), propane (C3H8) and finelydivided silicon dust are flammable and / or explosive in certain concentrations in an oxidantif an ignition source is provided. An ignition source could arise, for example, from a localisedheat build-up. This is discussed in Section 6.8Sources of ignition Sources of ignition on page24.

You can avoid the explosion hazard by ensuring that the concentration of the potentiallyflammable mixture is kept outside the flammable zone. Further details are given in Section6.5Avoiding the flammable zone Avoiding the flammable zone on page 21.

Another method you may be able to use to reduce the probability of explosion is toeliminate the ignition source. Further details are given in Section 6.8Sources of ignitionSources of ignition on page 24.

Where it is not possible to avoid the flammable zone, you must ensure that the equipment isdesigned to avoid or to contain any resulting explosion without rupturing or transmitting aflame to the outside atmosphere. The use of flame arrestors is discussed in Section 6.7Useof flame arrester protection systems Use of flame arrester protection systems on page 24. Ifthe external atmosphere of your vacuum system is hazardous you must ensure that allequipment is suitably rated for it.

Within the European Union the ATEX directive gives clear guidance on the design ofequipment that is to be used in potentially explosive atmospheres.

Where it is possible to avoid pumping potentially explosive atmospheres under allconditions, all types of Edwards vacuum pumps may be used to pump flammable vapours orgases.

Pyrophoric materials

Under most conditions, pyrophoric gases such as silane (SiH4) and phosphine (PH3) orpyrophoric dusts spontaneously react with air at atmospheric pressure, so that combustioncould occur when these gases come into contact with air, or other oxidant, where thepressure is sufficiently high to support combustion. This can happen if air leaks into thesystem or if the system exhaust comes into contact with the atmosphere. The heat from thereaction of an oxidant and pyrophoric gas can act as an ignition source for explosivematerials.

If exhaust gases from different processes are vented through a common extraction system,combustion and / or an explosion could result. It is therefore recommended that you useindependent extraction systems when you pump pyrophoric materials.

Processes that use phosphorus may cause solid phosphorus to condense in the vacuumsystem or its exhaust. In the presence of air and subject to even slight mechanical agitation(for example, activation of a valve or pump rotation caused by a pressure differential),phosphorus can spontaneously burn to release toxic gases. It is recommended that pumps

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are operated with an inert gas purge and run sufficiently hot to minimize the condensationof phosphorus.

PFPE lubricants can absorb process gases which, in the case of pyrophoric materials, canlead to local ignition when the lubricant is exposed to air. This hazard can becomeparticularly apparent during servicing, or where an oxidant is pumped through the systemafter a pyrophoric gas or dust. You can reduce the probability of an occurrence of this hazardif you use Edwards dry pumps which contain no lubricants in the swept volume. You mustensure that all pyrophoric material has been passivated before it is vented or handled.

Sodium azide

Sodium azide is occasionally used in the preparation of products for freeze drying and inother manufacturing processes. Sodium azide can produce hydrozoic acid. Hydrozoic acidvapours can react with heavy metals to form unstable metal azides. These azides mayexplode spontaneously.

The heavy metals include:

• Barium • Cadmium • Caesium• Calcium • Copper • Lead• Lithium • Manganese • Potassium• Rubidium • Silver • Sodium• Strontium • Tin • Zinc• Copper and zinc alloys (such as brass)

Brass, copper, cadmium, tin and zinc are commonly used in many components in vacuumpumps, accessories and pipes. If your process system uses or produces sodium azide, youmust ensure that the gas path in your process system does not contain heavy metals.

Toxic or corrosive materials

Many vacuum applications involve the processing and handling of toxic and corrosivematerials and require specific procedures.

Toxic materials

Toxic materials by their nature are hazardous to health. However, the nature of the hazard isspecific to the material and its relative concentration. You should comply with correcthandling procedures provided by the supplier of the material and applicable legislation.

You should also consider the following points:

▪ Gas dilution - Facilities exist to allow dilution of toxic process gases as they passthrough the vacuum pump and into the exhaust. You may use this dilution toreduce the concentration below the toxic limit. We recommend that you monitoryour dilution gas supply to alarm if the supply fails. Specifically for oil sealedpumps, refer to the pump instruction manual for possible oil return kits required.

▪ Leak detection - Edwards vacuum systems are generally designed to be leak tight -to a level of < 1 x 10-3 mbar l s-1 (< 1 x 10-1 Pa l s-1). However, the leak tightnessof the adjoining system cannot be ensured. You must use a suitable leak detectionmethod (for example, helium mass spectrometry leak detection) to confirm theintegrity of the vacuum and exhaust system.

▪ Shaft sealing (Edwards dry pumps) - Many dry vacuum pumps use a gas purgesystem to ensure process gases do not enter the gearbox and bearings and therebypotentially the atmosphere surrounding the vacuum system. You must ensure the

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integrity of this gas supply when handling toxic materials. Non-venting regulatorsmust be used in combination with a non-return check valve, as discussed inSection 7.4.3Pressure regulators Pressure regulators on page 29.

▪ Shaft sealing (Edwards other pumps) - Oil flooded shaft-seal designs (for example,EH mechanical booster pumps and EM rotary vane pumps) minimize the risk ofprocess gas leakage (or of the in-leakage of air), and can give a visual warning (oilleakage or oil level reduction) before a hazard arises. Other seal designs may notgive adequate warning of failure.

▪ Magnetic drives - Where total hermetic sealing is required, Edwards EDP dryvacuum pumps can be supplied fitted with a magnetic drive employing a ceramiccontainment vessel which eliminates the need for shaft sealing on the motor inputshaft.

If pressure relief valves or bursting disks are used to relieve excess pressure, ensure that theyare safely vented into a suitable exhaust system, which prevents a toxic hazard.

When you return contaminated vacuum equipment to Edwards for service or maintenance,you must follow the specific procedures (Form HS1) and complete the declaration (FormHS2) given in the Instruction Manual supplied with the equipment.

Corrosive materials

When pumping corrosive materials with Edwards vacuum pumps, you should take note ofthe following points:

▪ Moisture ingress - You must take special care to prevent the ingress of moist airwhich can accelerate corrosive effects. An inert purge should be used as part of theshut down procedure in order to flush corrosives out of the system prior to shutdown.

▪ Dilution - Use a suitable inert dilution gas to prevent condensation of corrosivesand hence mitigate the resulting corrosion.

▪ Temperature - Increase the pump and exhaust line temperature to preventcondensation of water vapour which can therefore limit corrosion. In some caseshigher temperatures can increase corrosion rates, please refer to the paragraphbelow.

▪ Corrosion of safety equipment - Where safety critical equipment (such as flamearrestor elements, temperature sensors and so on) could be damaged by corrosiveproducts in the process gas flow, their materials of construction must be selectedin order to remove this hazard.

▪ Phase changes - Unplanned phase changes can result in condensation.Consideration of changes in temperature and pressure is required to avoid thishazard.

▪ Unplanned reactions - Unplanned chemical reactions can lead to the generation ofcorrosive products. Careful consideration should be given to the possibility of crosscontamination when equipment is used for more than one purpose.

Some corrosive materials such as fluorine, chlorine, other halogens or halides and oxidizingagents such as Ozone or reducing agents such as Hydrogen sulfide can also attack thematerials they are in contact with, without the need for any liquid to be present. In thesecases the partial pressure of the corrosive material should be minimized through the use of asuitable dilution gas. The materials of construction of the vacuum system and the pumpmodel should be selected as being compatible with the particular gas in the concentrationsexpected. High temperatures can accelerate corrosion and so should be minimized whereother process considerations allow. Maintenance intervals should be reviewed to considerthe effect of corrosive materials on the system.

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Summary - chemical sources of hazards

▪ Consider all possible chemical reactions within your system.▪ Make allowance for abnormal chemical reactions, including those which could

occur under fault conditions.▪ Refer to Material Safety Data Sheets when you assess the potential hazards

associated with your process materials.▪ Use dilution techniques to minimize reactions with oxidants and flammable

materials.▪ In the EU where a flammable zone has been specified, you must use a suitable

certified ATEX vacuum pump. For all other regions Edwards recommends the useof pumps that have been certified under the ATEX directive wherever possible.

▪ Use the correct type of lubricant in your pump when you pump oxidants, andconsider the use of a dry pump.

▪ Do not use heavy metals in the gas path of your process system if your processuses or produces sodium azide.

▪ Take specific care when handling toxic, corrosive or unstable materials.

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Physical sources of hazards

Types of over-pressure hazard

The over-pressure of components in a vacuum system can be a result of any of the following:

▪ the introduction of high pressure gas into the system▪ the compression of gas by the system▪ a sudden increase of temperature of volatile gas in the system▪ a phase change leading to the deposition of solid product▪ reaction inside the vacuum system▪ blocked exhaust.

Other causes are possible.

Over-pressurised pump exhaust

A common cause of an over-pressurised exhaust is a blockage or restriction in the exhaustsystem. This can lead to failure of the pump or other components in the system.

Vacuum pumps are compressors which are specifically designed to operate with high outlet-to-inlet compression ratios.

In addition to the potential over-pressure caused by the operation of the pump, theintroduction of a compressed gas (such as a purge or dilution gas) can also over-pressurisethe system if the exhaust system is restricted or blocked.

Where a pump is fitted with flame arrestors or other equipment like filters or condensers onthe exhaust side, it is essential that the exhaust back pressure does not exceed themaximum limit stated in the vacuum system Instruction Manual. A suitable maintenanceprogram should be employed to ensure that process deposits do not block the exhaustsystem and flame arrestor. If this is not practical, then a pressure sensor located betweenthe pump and the flame arrestor should be used to detect blockage. Similar considerationsshould be given to other exhaust equipment such as filters and condensers.

Sublimation or phase change can lead to blockage by solid deposits of process pipework andan over pressure hazard.

Refer to the Instruction Manuals supplied with the vacuum pumping system for maximumand recommended continuous back-pressures of all your exhaust components includingyour vacuum pump. Design the exhaust system so that these limitations can be met.

For limits during continuous operation please refer to the pump instruction manual.

Protection against exhaust over-pressure

We generally recommend that pumps are operated with the exhaust piped into a freelyvented exhaust system. However, your exhaust system may incorporate components whichmay cause a restriction or blockage of the system. If so, you must also incorporate suitablemethods of protection against over-pressure. Such methods include, for example:

Component Protection MethodValve in exhaust pipeline Interlock the valve so that it is always open

when the pump is operating.

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P40040100_E - Physical sources of hazards

Component Protection MethodIncorporate a pressure relief by-pass.

Exhaust scrubber Incorporate a pressure relief by-pass.Incorporate a pressure monitor and interlockthis with the pump so that the pump is switchedoff when the exhaust pressure is too high.

Flame arrestor Exhaust pressure measurement.Differential pressure measurement.

Oil mist filter Incorporate a pressure relief device.

To summarize, if the pressure in the exhaust system approaches the maximum allowablepressure:

▪ Reduce the pressure by a device in a gas path parallel with the restriction orblockage.

▪ Reduce the source of the pressure. Stop the pump or shut down any compressedgas supplies.

Inlet over-pressure

Compressed gas supplies and back pressure

It is common to underestimate the required pressure rating of the pipeline connecting thepump to the vacuum system, due to the belief that this pipeline will not be subjected topressures above atmospheric pressure. In practice, this is only true under normal designoperating conditions. You should estimate the required pressure rating to allow for higherpressures caused by abnormal or fault conditions.

A common cause of over-pressure in pump inlet pipelines is the introduction of compressedgases (such as purge gases) when the pump is not operating. If components in the inletpipeline are not suitable for the pressures which result, the pipeline will rupture and processgases will leak from the system. A back flow of gases from the system into a processchamber which itself is not capable of withstanding the pressure which results, will alsocause ruptures and leaks.

When you connect compressed gas supplies to your system through pressure regulatorswhich are designed to provide a low pressure flow, ensure the pressure is within the ratingof the system.

The non-venting pressure regulators commonly used will cause the pressure within thesystem to rise to the pressure of the gas supply to the regulator, if operated under conditionswhere there is no process gas flow through the system. You must therefore use one of thefollowing two methods to prevent over-pressurisation:

▪ reduce the pressure, allow the gases to by-pass the pump and flow into a freelyvented exhaust

▪ monitor the pressure of the system and use a positive closure valve to shut off thesupply of compressed gas at a preset pressure level.

Incorrect pump operation

Special precautions must be taken until it has been established that the pump is operatingcorrectly.

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If the direction of rotation of the pump is incorrect and the pump is operated with the inletblocked or restricted, the pump will generate high pressure in the inlet pipeline. This couldresult in rupture of the pump, the pipelines and / or components in the pipeline.

Always use a blanking plate loosely secured by screws to the pump inlet until you haveestablished that the direction of rotation of the pump is correct.

Operation at high rotational speeds could result in pump break up. Do not operate the pumpat rotational speeds above the maximum designed speed of rotation; this is particularlyimportant where frequency inverters are used for speed control.

Summary - physical sources of hazards

▪ When you perform safety calculations, ensure that the safe working pressures forall components in the system are taken into account.

▪ Ensure that the pump exhaust cannot become blocked or restricted.▪ If there is a risk of high pressures in excess of the pressure rating of any part of

your vacuum system occurring, we recommend that your system incorporatessuitably positioned pressure measuring equipment. This must be connected toyour control system to put your system in to a safe state, if an over-pressurecondition is detected.

▪ Take account of abnormal and fault conditions when you assess the requiredpressure rating of the vacuum system and pump components.

▪ Ensure that you incorporate the correct type of pressure relief device and that it issuitably rated for your application.

▪ Ensure that compressed gas supplies are properly regulated and monitored. Switchoff these supplies if the pump is switched off.

▪ Where possible, ensure the supply pressure to any regulated purges is lower thanthe maximum allowable static pressure of the system. Alternatively, ensure thatpressure relief is possible in the event of component failure.

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Hazard analysisThe techniques of hazard analysis provide a structured approach to the identification andanalysis of the hazards in a system in normal use, and the hazards which may arise underfault and failure conditions. Such techniques provide a route to hazard management; the useof these techniques may, in many circumstances, be a statutory / legal requirement. To befully effective, hazard analyses must begin during the initial design of a system and mustcontinue through the installation and operation, as well as the maintenance anddecommissioning of the system.

A detailed study of hazard analysis techniques is beyond the scope of this publication. Thereare, however, many hazard analysis techniques described elsewhere. An example of atechnique commonly used in the chemical processing industry is HAZOP (Hazard andOperability Study). This is a procedure for hazard analysis which is concerned with theidentification of potential hazards and operating problems.

Typically, hazard analyses generate information about the type of hazards, the severity ofthese hazards, and the probability that the hazards will occur. This information can be usedto decide on the best way to reduce the effects of the hazards to acceptable levels.Depending on the origin of the hazard, it may be possible either to eliminate the hazard, orto reduce the severity of the hazard, and / or to reduce the probability that the hazard willoccur. It is, however, rare that hazards can be eliminated completely.

You must consider all possible effects of a hazard when you decide on the best way tomanage the hazard. For example, a small hot surface may present a minor hazard for anoperator as it could cause a burn. To reduce the probability of the occurrence of a burn, thesystem designer may provide a visible warning of the hot surface, or may put a guard aroundthe hot surface. However, the hazard analysis of the system may also indicate that the samehot surface could provide a source of ignition for flammable vapours; this might lead to anexplosion or to the release of a toxic vapour cloud. To reduce the probability of ignition, thesystem designer must reduce the temperature of the hot surface, or ensure that theflammable vapours cannot contact the hot surface.

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P40040100_E - Hazard analysis

System design

Pressure ratings in a system

As discussed in Section 4 Physical sources of hazards Physical sources of hazards on page15vacuum system pipelines and components are designed to work with internal pressuresbelow atmospheric pressure. In practice, however, it is usually necessary to design yoursystem for use with internal pressures above atmospheric pressure as well. If necessary, youmust incorporate pressure relief devices to prevent over-pressurisation.

It is important that you do not allow the inlet pipes and other inlet components to becomethe weakest part of the system, on the assumption that they will always operate undervacuum, even under fault conditions.

Exhaust systems must always be designed to offer the smallest possible back-pressure to thepump during operation. It is important, however, that you design your exhaust system withan adequate pressure rating; it must be suitable for use with the pressures that can begenerated by the pump and also for example by the introduction into the system of acompressed gas, and be suitable for use with the over-pressure protection measures used.

When you perform your hazard analysis, you should always consider:

▪ External inlets, such as inert gas connections▪ Isolation and constriction from all sources, especially in exhaust lines▪ Reactions between process gases.

It should be noted that where a vessel contains a volatile liquid and can be isolated from therest of the system, then the application of external heat (for example, from a fire) may resultin internal pressures greater than the design pressure of the vessel. You must consider theneed for suitable pressure relief in this case.

Elimination of stagnant volumes

A stagnant volume is any volume in a vacuum pipe or component which is not subjected to athrough flow of gas. Examples are the gear box of a mechanical booster pump or the gaugehead of an instrument. Valved pipework and nitrogen gas inlet pipes can also becomestagnant volumes when they are isolated

Stagnant volumes must be taken into account when you consider the mixture and reactionof process gases which are not normally present together in the process chamber. Pipes,pumps and process chambers generally transport gases linearly, with one gas or gas mixturefollowed by another. Gases transported in such linear flows are not normally mixed unlessthe velocity of the exhaust gas is reduced by a restriction or blockage. A stagnant volume isnot purged and may be filled with process gases as the pressure in the system rises and falls.In this way, gases which pass through the system at one stage of the process can be retained.These may then react with gases from a subsequent phase of the process. Thoroughevacuation of the chamber between the introduction of incompatible gases will guardagainst the risk of explosion.

You must take special care when considering cross-contamination in stagnant volumes andwhen the gases are potentially explosive. In particular, you should consider the hazard ofbuild-up in filters and separators and other components. Where appropriate, use highintegrity, continuous flows of inert purge gas to reduce the probability of crosscontamination.

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P40040100_E - System design

When pumping flammables, it is possible for stagnant volumes to fill with potentiallyexplosive gases or vapours that cannot be removed by normal purging. Where an ignitionsource could also be present, specific purging of the stagnant volume should be considered.

Exhaust extraction systems

It is important that you use the correct type of exhaust extraction system for your process.As previously stated, the extraction system must be designed to withstand the pressures ofoperation and, when hazardous materials are produced or processed, must be sufficientlyleaktight to contain the process materials and their by-products and prevent hazardousreleases to atmosphere.

Sources of potentially explosive gas or vapour mixtures

When a flammable gas or vapour is mixed with the correct concentration of oxygen or othersuitable oxidant, it will form a potentially explosive mixture which can ignite in the presenceof an ignition source.

While it is generally apparent if a pumped material is potentially explosive, there are, in theexperience of Edwards, some conditions where a potentially explosive mixture is produceddue to conditions which were not considered during the design of the system for theprocess. You must identify all possible process conditions and possible sources of potentiallyexplosive mixtures which could be generated by your equipment. Some examples fromEdwards experience are listed below, but the list is by no means exhaustive:

▪ Cross contamination - Where a vacuum pump is being used for a number ofduties, it is possible that its use with individual materials is safe, but if the pump isnot purged before use with another material, then cross contamination couldoccur with unexpected reactions.

▪ Cleaning fluids - An application may be viewed as benign, but the use offlammable cleaning fluids and the subsequent drying by evacuation through thevacuum pump can create a potentially explosive mixture.

▪ Unexpected materials - On 'house vacuum' duties where the vacuum pump isused to provide a distributed vacuum system, it is possible to pump flammablematerials which were not considered during the system design. These materialsmay have auto-ignition temperatures lower than the internal temperatures ortemperature rating of the vacuum pump.

▪ Dissolved vapours - These can evolve during process operation, and care needs tobe taken to select the correct internal Temperature rating for your process.Typically in the Chemical process market, this is covered by ATEX requirements.

▪ Air leakage - The accidental ingress of air or oxidant into a system may change theconcentration of a flammable gas or vapour and create a potentially explosivemixture.

▪ Flammable sealing liquids - Where a flammable liquid is used as the sealing liquidin a liquid ring vacuum pump, the ingress of air will create a potentially explosiveinternal mixture.

▪ Condensed process materials - If there is the possibility of flammable materialcondensing inside your system, you must be aware that they could react withoxidants from other process steps or with air (for example in the exhaust). This canbe avoided by suitable temperature or partial pressure control.

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Avoiding the flammable zone

A flammable material will only create a potentially explosive atmosphere if it is combinedwith air or oxygen or other oxidant and its concentration lies between the LowerFlammability Limit - LFL (or Lower Explosion Limit - LEL) and the Upper Flammability Limit -UFL (or Upper Explosion Limit - UEL). Please note that most data found in literature refers toflammability limits in air, i.e. where oxygen is the oxidant. All further information givenbelow will be based on that assumption.

To be potentially explosive, it is also necessary for the concentration of oxygen to be abovethe Minimum Oxygen Concentration - MOC (or Limiting Oxygen Concentration - LOC). TheMOC (LOC) for the majority of flammable gases is 5 % vol. or greater. (Note: This does notapply to pyrophoric materials which require special precautions.)

There are a number of strategies that can be used to avoid operating with gas mixtures inthe flammable zone. The choice of strategy will depend on the outcome of the riskassessment (hazard analysis) for the process and the pumping system:

▪ Maintain the flammable gas concentration below the LFL (LEL)To minimize the risk of the flammable gas accidentally entering the flammablezone, a safety margin for below-LFL (LEL) operation should be used.A safety margin should be determined by the user following a risk assessment.Some authorities suggest maintaining the concentration at below 25 % LFL (LEL).The commonly used method of maintaining a suitable concentration below LFL(LEL) is dilution with inert gas purge (for example, nitrogen), introduced into thepump inlet and/or purge connections. The required integrity of the dilution systemand of any alarms or interlocks will depend on the hazardous zone which wouldresult if the dilution system were to fail.

Note:

Ensure that suitable precautions are taken to avoid the risk of asphyxiation.

▪ Maintain the oxygen concentration below the MOC (LOC)This mode of operation requires the use of oxygen concentration monitoring of thepumped gases to ensure safe operation. To minimize the risk of the flammable gasaccidentally entering the flammable zone, a safety margin for below-MOC (LOC)operation should be used. Available industry standards indicate that where theoxygen concentration is continuously monitored, it should be maintained at lessthan 2 volume percentage points below the lowest published MOC (LOC) for thegas mixture. Unless the MOC (LOC) is less than 5 %, the oxygen concentration mustbe maintained at no more than 60 % of the MOC (LOC). If monitoring is onlyundertaken in the form of routine oxygen level checks, the oxygen level should notbe allowed to exceed 60 % of the lowest published MOC (LOC) unless the MOC(LOC) is less than 5 %, in which case the oxygen concentration must be maintainedbelow 40 % of the MOC (LOC).The preferred method of maintaining the oxygen level below the lowest publishedMOC (LOC) is by the rigorous exclusion of air and oxygen from the process andpump system, together with dilution of the pumped gas with an inert purge gas(such as nitrogen), introduced into the pump inlet and/or purge connections, ifneeded. The required integrity of the air/oxygen exclusion measures and of anyalarms and interlocks will depend on the hazardous zone that would result werethe exclusion and dilution systems to fail.

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Precautions typically required to rigorously exclude air from the process and pumpsystem are given at the end of this section.

▪ Maintain the flammable gas concentration above the UFL (UEL)Where flammable gas concentrations are high, then operation above UFL (UEL) canbe more suitable. To minimize the risk of any accidental incursion into theflammable zone, a safety margin for above-UFL (UEL) operation should be used. Itis recommended that the residual oxygen level in the gas should be maintained atless than 60 % of the absolute oxygen level normally present at the flammable gasUFL (UEL) concentration.The preferred method of maintaining the oxygen level below this safety margin, isrigorous exclusion of air and oxygen from the process and pump system. Dilutionof the pumped gas with an inert purge gas (such asnitrogen) or with additional flammable gas ('padding' gas), introduced into thepump inlet and/or purge connections, may also be needed. The required integrityof the air exclusion measures, of any purge gas introduction system, and of anyalarms and interlocks will depend on the hazardous zone that would result werethe exclusion and dilution systems to fail.

▪ Maintaining the flammable gas concentration below the minimum explosionpressureEvery flammable material has got a minimum pressure below which an explosioncan't be sustained. If the pressure at the inlet to the vacuum pump can bemaintained securely below this pressure then ignitions starting inside the vacuumpump will not be able to spread to the inlet. Precautions, however, must be takenfor the exhaust of the vacuum pump.Precautions typically required to rigorously exclude air from the process and pumpsystem are as follows:

▪ Elimination of air leaksUse a leak detector or conduct a pressure ‘rate-of-rise’ test. Before admittingflammable materials into the process chamber, it is possible to perform a test toestablish that air (oxygen) leakage into the vacuum system is within allowablelimits.To perform a pressure ‘rate-of-rise’ test, the empty process chamber is evacuatedto a pressure just below the normal operating pressure, and is then isolated fromthe vacuum pump. The pressure in the process chamber is then recorded over afixed period of time. As the volume of the process chamber is known along withthe maximum allowable air leakage, it is possible to calculate a maximumallowable pressure rise that can occur over the fixed period of time. If thismaximum pressure limit is exceeded, action must be taken to seal the source ofthe air (oxygen) leakage into the process chamber; the test must then be repeatedsuccessfully before the admission of flammable materials into the processchamber is allowed.In some cases, the ability of the vacuum system to achieve a good base pressurecan be used to indicate system leak tightness.

▪ Remove all air from the system before the start of the processBefore any flammable gas is admitted into the process, the system should be fullyevacuated and/or purged with inert gas (such as nitrogen), to remove all air fromthe system. At the end of the process, repeat this procedure to remove anyflammable gas before the system is finally vented to air.

▪ For dry vacuum pumps

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Ensure that any shaft or purge seal gas cannot be supplied or contaminated withair under any circumstances, and ensure that any gas ballast port is either sealed,or only used to introduce inert gas.

▪ For wet vacuum pumps (e.g oil sealed rotary piston or rotary vane pumps)Maintain the shaft seals fully in accordance with the manufacturer's instructions,and use a pumped and pressurised oil lubrication system with an alarm indicationfor loss of oil pressure. This system may comprise an external accessory to providefiltered and pressurised lubricating oil, with a pressure switch. Ensure that any gasballast port is either sealed, or only used to introduce inert gas. Provide anadequate purge of inert gas to the oil box, to remove air before the start of theprocess.

▪ For roots vacuum booster pumpsMaintain the primary drive shaft seal fully in accordance with the manufacturer'sinstructions, and ensure that any purge or ‘breather’ port connections can only beused to introduce inert gas.

▪ Reverse flowEnsure that the system operating procedures and facilities protect the system fromany reverse air flow which might result from a pump failure. Ensure that anypumped flammable gases are safely disposed of at the final vent from the pumpexhaust. Ensure that flammable gas mixtures cannot arise in the exhaust pipeline,by the use of suitable inert purging of the pipeline before the start of and after theend of the flammable gas process, and by the use of adequate inert gas purgingduring operation, to prevent turbulent back-mixing of air down the exhaust.

Levels of system integrity

Methods of protection using inert gas dilution have been discussed in earlier sections. Theprinciple of the method is that you mix an inert gas (usually nitrogen) with your processgases to dilute them to a level where an explosion or reaction cannot occur. When you usegas dilution as a primary safety system to protect against possible explosion, you mayrequire a high integrity alarm and interlock system to prevent the operation of the systemwhen the gas dilution system is not operational. The integrity of the gas dilution systemshould be considered during the risk assessment (hazard analysis), and will depend on theinternal zoning (i.e. level of risk) which would result were the dilution system to fail. Currentbest practice should always be applied to this risk assessment, to determine the requiredlevels of system integrity.

For example, if a dilution system were used to maintain a flammable gas concentrationoutside the flammable zone, and the result of dilution failure would be that the pumped gaswould be inside the flammable zone, continuously or for long periods of time (typically ATEXZone 0 requirement would consider >50 %), then the dilution system must satisfy one of thefollowing:

▪ It must be failsafe even in the event of rare malfunction▪ It must be safe with two faults present▪ It must comprise two independent dilution supply systems.

Alternatively, if the result of dilution system failure would be that the pumped gas would beinside the flammable zone occasionally (typically ATEX Zone 1 condition), then the dilutionsystem must satisfy one of the following:

▪ It must be failsafe even in the event of expected malfunction▪ It must be safe with one fault present.

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If the result of dilution system failure is that the pumped gas would be unlikely to enter theflammable zone, or might do so only for brief periods (typically ATEX Zone 2 condition), thenthe dilution system must be safe in normal operation.

Use of flame arrester protection systems

If the mixture of pumped gases and vapours is flammable (see Section 6.5Avoiding theflammable zone Avoiding the flammable zone on page 21) continuously or for long periodsof time (i.e Zone 0 condition) and if there is a risk of an ignition source (see Section6.8Sources of ignition Sources of ignition on page 24) becoming active during normaloperation or foreseeable malfunction you must fit flame arresters as required to yourprimary pump (also see Section 7.4.4Flame arresters Flame arresters on page 30). Thirdparty certification has been obtained for the use of specific flame arresters with Edwardsvacuum pumps, demonstrating their ability to prevent flame transmission along the processpipework or into the surrounding atmosphere.

Where the flammable mixture is present for long periods of time an approved and testedtemperature transmitter has to be installed on the inlet flame arrester to detect acontinuous burn. If a continuous burn is detected the pump needs to be switched off andisolated from the fuel source. Please contact Edwards for advice on approved flame arrestersand temperature transmitters. In order to protect the flame arrester and pump thermallyunder rare malfunctions (Zone 0) of the pump, an exhaust temperature transmitter must beinstalled in the exhaust of the pump. Switch off points are dependant upon pumpingsystems. Please consult the relevant ATEX manual for the pump.

If either temperature transmitter on the inlet or exhaust reach their maximum limit,indicating a fault condition, then suitable actions must be taken. This is applicationdependent but could include:

▪ Stopping the supply of fuel - Closing a valve located on the inlet of the vacuumpump will prevent the supply of fuel into the vacuum pump

▪ Stopping the source of the ignition - Stopping the vacuum pump by turning off thepower to the motor

▪ Inerting the area of the burn - The rapid addition of inert gas into the area of burn(typically, but not always located in the exhaust manifold of the pump), willeliminate the flame. Note that it is possible for a flame to re-ignite if the source ofignition is not removed.

Sources of ignition

Where vacuum pumps are used to pump flammable mixtures, you must consider all possiblesources of ignition. Below are some areas of consideration which you can use as part of anoverall review. Depending upon your process you might be able to avoid some or all ignitionsources. If are unable to avoid the ignition source because of your process condition orsystem requirement, you must then design your system accordingly.

Note:

Some Edwards pumps are certified by a third party to confirm that (if correctly applied) theywill contain an internal explosion.

▪ Mechanical contact - Mechanical contact of rotating and stationary parts insidethe vacuum pump and system could provide an ignition source. All Edwardsvacuum pumps are designed and built to keep the correct running clearancesinside the pump during all operating conditions. To avoid this ignition source it is

Page 24


important to avoid deposition of materials on the internal surfaces or to clean thepump. The bearings must be kept in good condition, have sufficient lubrication andsuitable purge gas to eliminate contact with process gases. The recommendedmaintenance regime for the bearings must be followed to ensure safe and reliableoperation.

▪ Particle ingestion - All pumping mechanisms have the potential to ingest particleswhich have been created by the process or which are a result of the systemmanufacturing process. Where these are rolled between a moving surface and astatic one, it is possible to generate heat. A suitable inlet screen (mesh) or filterwill prevent the ingress of particles into the vacuum pump to reduce the size andvolume of particles to a safe amount. Care must be taken to have a suitablemaintenance regime for the inlet screen.

▪ Dust build up - The build up of fine compacted dust within internal clearances canoccur where any pumping mechanism is placed on a dust generating process. Evenwith the use of inlet dust filters, it is still possible for small dust particles to enterthe pump. With small dimensional changes due to thermal changes, compacteddust can touch a moving surface and create heat.

▪ Heat of compression (auto-ignition) - The internal heat of compression within anycompressor must be considered in relation to the auto-ignition temperature of anygases or vapours which are pumped. You must ensure that the pump has atemperature classification that is at least the same or higher than the gases youare pumping.

▪ Hot surfaces - Where flammable gases or vapours are allowed to come intocontact with a hot surface, they may ignite if the auto-ignition temperature isexceeded. Note: Edwards pumps and flame arrestors should not be thermallyinsulated if this could cause increased surface temperatures internally (andexternally) leading to auto-ignition.

▪ Externally applied heat - Externally applied heat can occur, for example, in theevent of a fire in the immediate area of the vacuum equipment. Under thiscondition, it is possible to generate internal pressures in excess of the maximumstatic pressure of the system, and temperatures in excess of auto-ignitiontemperature. This should be considered as part of the system hazard analysis.

▪ Hot process gas flow - High inlet gas temperatures can lead to internal (orexternal) surfaces exceeding the auto-ignition temperature of the materials beingpumped. High temperature inlet gas can also lead to rotor/ stator seizure. Pleaseconsult your vacuum pump instruction manual for maximum allowable internal gastemperatures. Consult Edwards for further advice.

▪ Catalytic reaction - The presence of certain materials can lead to catalytic ignition.All materials of construction in the vacuum system should be considered for theirpotential to act in this way with the pumped gases or vapours.

▪ Pyrophoric reaction - The heat of combustion of pyrophoric materials caused byair or oxidant ingress could act as an ignition source for any flammable materialpresent. See Pyrophoric materials on page 11.

▪ Static electricity - Certain conditions can occur where static electricity can build upon insulated components before discharging to earth in the form of a spark. Thepotential for static build-up should be considered as part of the system design.

▪ Lightning - Where located in an outdoor location, a lightning strike can provideignition energy. The potential of this event occurring should be considered as partof the system design.

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Summary - system design

In order to design safe vacuum pumping systems, the following points must be taken intoconsideration. Depending on your application, there may be others.

▪ If you pump hazardous materials, you must design the system to fail to a safecondition

▪ Use PFPE (perfluoropolyether) lubricants in pumps when you pump oxidants▪ Where inert gas is used to reduce the concentration of the flammable gas below

the lower explosion or flammability limit or below the minimum or lower oxidantconcentration you must ensure the integrity of the inert gas supply

▪ The concentration can also be kept above the upper explosion or flammabilitylimit, but suitable safety precautions need to be put in place to ensure that theconcentration cannot fall into the flammable range

▪ Leak test systems and equipment to ensure required leak tightness before use▪ Dilute pyrophoric gases to safe levels with an inert gas before the gases are

exhausted to atmosphere or mixed with oxidant gases▪ You must not allow contact between sodium azide and heavy metals anywhere in

the gas path of your system▪ You must not allow the maximum pressure of the system to exceed the individual

safe level of any single part of the system▪ You must always consult the safety information supplied for the substances which

you intend to pump▪ Consider the use of dry pumps in preference to oil sealed rotary vane or piston

pumps where there are hazards associated with the oil in the swept volume▪ Where Edwards vacuum pumps are used to pump potentially flammable mixtures,

you must consider all possible sources of ignition and the potential consequenceof a possible explosion.

Page 26


The correct choice of equipmentTo ensure that you choose the correct equipment for your application, you must considerthe limits within which you will require the system to operate. The technical data forEdwards equipment is given in our Product Catalogue, Marketing Publications and in theequipment's Instruction Manual(s). In most instances, further information is available onrequest; please contact Edwards for further advice.

When you design your vacuum system, take account of the relevant mechanical pumpparameters, for example:

▪ Maximum static pressure (inlet and exhaust)▪ Maximum operating inlet pressure▪ Maximum operating exhaust pressure▪ Conductance of the inlet and exhaust components▪ Pressure specification of other components fitted to the pump▪ Pressure monitoring in case the exhaust line becomes blocked.

For oil-sealed rotary vane and piston pumps, you must also consider for example:

▪ Gas ballast flow rate▪ Oil box purge flow rate▪ Gases and vapours trapped in the oil box▪ Gases and vapours absorbed into the oil in the oil box.

The maximum static pressure defines the maximum pressure to which an inlet or outletconnection of a pump can be exposed when the pump is not operational. The pressure isdependant on the mechanical design of the pump.

Oil-sealed rotary vane and piston pumps are designed to operate with inlet pressures at orbelow atmospheric pressure and, even though the maximum static pressure rating may beabove atmospheric pressure, the maximum inlet pressure of the pump when it operatesmust not be allowed to go above atmospheric pressure. Some manufacturers limit thecontinuous inlet pressure of their pumps to pressures below atmospheric pressure. Themaximum inlet pressure with the pump in operation is referred to as the maximumoperating pressure.

The reason that the maximum operating pressure is limited, is not necessarily related to themechanical integrity of the pump. The maximum pressure is usually proportional to thepower rating of the pump at high inlet pressures, and is associated with the potential hazardof overheating the mechanical components of the pump or the electric motor.

For similar reasons, we recommend that you maintain the outlet pressure of your vacuumpump as low as possible (typically at or below 0.15 bar gauge, 1.15 x 105 Pa, for continuousoperation). Pumps are designed to operate with unrestricted exhausts and an outletpressure of 0.15 bar gauge (1.15 x 105 Pa) is usually high enough to drive exhaust gasesthrough your exhaust extraction system and treatment equipment.

Oil-sealed rotary vane and piston pumps

Edwards oil-sealed rotary pumps include the E1M, E2M, ES and RV series rotary vane pumps,and the Stokes Microvac range of oil sealed piston pumps. Generally, all vacuum pumps aredesigned to operate with inlet pressures below atmospheric pressure and with the pumpexhaust freely vented to atmosphere.

Page 27

P40040100_E - The correct choice of equipment

Oil-sealed rotary vane and piston pumps are positive displacement compressors and cangenerate very high exhaust pressures if the outlet is blocked or restricted. In these cases, thepressures can exceed the safe static pressure of the pump oil box and, in many instances, thesafe static pressures of downstream components in the system (such as polypropylenescrubbers or vacuum O-ring joints). Therefore Edwards strongly recommends that you fit ahigh integrity exhaust pressure sensor in the pump exhaust line.

To achieve a safe level of dilution, the gas ballast can be augmented by an oil box purge(where this facility is available) connected to the oil box on the pump. An increase in the gasballast and oil box purge flow rates increases the amount of oil carried over to the exhaustsystem.

All Edwards oil-sealed pumps have significant oil box volumes which can retain flammableand explosive gas mixtures. The oil in the oil box can effectively absorb or condense vapourand gaseous by-products. The vapours and gases trapped in the oil may be pyrophoric ortoxic. You must, therefore, have special handling procedures to ensure safety duringmaintenance.

Edwards dry pumps

The maximum operating pressure is limited by the same factors that affect oil-sealed pumps(that is, the potential hazard of overheating the mechanical components of the pump or theelectric motor).

Edwards dry pumps are positive displacement compressors and can generate high exhaustpressures. When the pumps are incorporated into a system where the process can result insolid by-products, (and so there is a possibility of a blockage in the exhaust line), Edwardsstrongly recommends that you fit a high integrity exhaust pressure monitor. Consult thepump Instruction Manual for the operating pressures to which the switches should be set.

Edwards dry pumps have a high-throughput gas ballast capability. The addition of a dilutiongas such a nitrogen can be made into the pump mechanism to optimise reactionsuppression. Please refer to your pump instruction manual for gas purge flow rates.

Pipeline design

Bellows

Bellows are short, thin walled components with deep convolutions. They are used to reducethe transfer of vibration from a pump to your vacuum system.

Always install bellows in a straight line with both ends rigidly constrained. When installedcorrectly, the bellows can withstand a small positive internal pressure (refer to theInstruction Manual supplied with your bellows for details). Do not use bellows on dry pumpexhausts; use braided flexible pipelines (see Section 7.3.2Flexible pipelines Flexible pipelineson page 28).

Consider the possibility of bellows fatigue failure when used on frequent cycle applications.

Flexible pipelines

Flexible pipelines have a thicker wall section and shallower convolutions than bellows.Flexible pipelines provide a convenient method for the connection of vacuum systemcomponents and help to compensate for misalignment or small movements in rigid vacuumpipelines. Flexible pipelines can be formed into relatively sharp bends and will hold theirposition.

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Flexible pipelines are intended for installation in static systems. They are not suitable forrepeated flexing which could cause fatigue failure.

When you use a flexible pipeline, use the shortest possible length and avoid unnecessarybends. For applications where high exhaust pressures can occur, braided flexible pipelinesshould be used.

Braided flexible pipelines are bellows with an outer protective layer of woven stainless steelbraid. When you install a braided flexible pipeline, you must observe the minimum bendradius given in the Instruction Manual supplied with the braided flexible pipeline.

Anchor points

You must anchor pipelines and pipeline components correctly. For example, if you anchorbellows incorrectly, they will not reduce the vibration generated by the pump and this couldlead to fatigue in the pipelines.

Seals

Where there is the possibility of positive pressures occurring in any part of the vacuumsystem (even under failure conditions), you must use suitable seal types and materials whichare capable of withstanding the expected vacuum and positive pressures.

Physical over-pressure protection

As discussed previously, over-pressure can be caused by a restriction or blockage in yoursystem or in one of its components. The over-pressure may occur as a result of compressedgas flow from the pump or from external compressed gas supplies (such as those for adilution system). There are two main methods of system over-pressure protection: namelypressure relief and over pressure alarm / trip, which are described in the followingparagraphs.

Pressure relief

You may use bursting disks or pressure relief valves to relieve an over-pressure condition.The operating pressure of the device must be below the design pressure rating of thesystem. You must connect these devices with suitable pipelines to an area in which it is safeto vent your process gases and which does not have vent restrictions. If your processproduces solid by-products, the pressure relief devices must be inspected regularly to ensurethat they are not blocked or restricted. The design of such protection devices should takeinto account the effect of pressure pulsations on the fatigue life of the bursting disk or thelife of the valve.

Over pressure alarm/trip

This method of protection is often used by Edwards. This type of protection is recommendedfor any system, but may not be suitable for systems which produce solid by-products.

Pressure regulators

There are two main types of pressure regulators: venting and non-venting.

Venting regulators vent gas to atmosphere or to a separate vent line to maintain a constantoutlet pressure under no-flow conditions. Venting regulators are generally used wherepipeline integrity is of paramount importance.

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Non-venting regulators can only maintain a constant outlet pressure under flow conditions.

Under no-flow conditions, the outlet pressure of some regulators can rise to the level of thesupply pressure. The rate of rise is dependent on the characteristics of the regulator and thevolume to which its outlet is connected. The rise can take from a few minutes to severalmonths.

Pressure regulators are not designed to be shut-off valves and must be used in combinationwith a suitable isolator device (such as a solenoid valve) when isolation is required.Alternatively, you must take measures to safely vent excess pressures.

Flame arresters

Flame arresters are not explosion prevention devices. They are designed to prevent thepropagation of a flame front along a pipe or duct (please refer to Section 6.7Use of flamearrester protection systems Use of flame arrester protection systems on page 24). Flamearresters offer a large surface area and small conductance gaps to the flame front, and socause the flame to be quenched. Flame arresters are generally only suitable for use insystems which are used for clean gases or vapours.

The explosive energy of gas mixtures increases with pressure. Most flame arresters aredesigned to protect areas where the internal pressure does not exceed atmosphericpressure. You must ensure that the operating pressure in the exhaust extraction systemleading up to the flame arrester is not allowed to exceed the maximum operating pressure.However in the case of arrestors certified for use with Edwards Chemical dry vacuum pumps,please refer to the ATEX instruction manual for maximum allowable pressures. You must alsoconsider the maximum allowable back pressure of your vacuum pump.

Flame arresters operate by removing the heat of combustion from the flame front, andtherefore have a maximum safe operating temperature. You must not allow thistemperature to be exceeded by trace heating, insulation or the temperature of the gas flowpassing through them.

The ability of a flame arrester to arrest a flame depends on the speed of the flame front,which in turn depends on its distance from the source of ignition. When used with EdwardsChemical vacuum pumps they should be closely coupled to the inlet and exhaust. The use ofElbows and Tee pieces between the pump and the arrester is acceptable for some pumpsunder certain conditions. Please consult Edwards for advice.

Purge systems

Inert gas purge systems can be fitted to equipment in order to remove process gas remainingin the system after the end of a process cycle.

The correct use of purge can ensure that corrosive products are removed, preventing themfrom damaging the pump and more importantly damaging protective systems such as flamearresters. In addition, the removal of process gases ensures that undesired and potentiallydangerous chemical reactions do not occur between materials used on different processcycles.

Summary - the correct choice of equipment

▪ Select the correct type of equipment for your application▪ Incorporate all of the appropriate safety devices necessary to ensure safety in the

event of a failure▪ Eliminate stagnant volumes

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▪ Ensure that the system is suitably controlled and regulated▪ Where appropriate, incorporate pressure relief devices▪ Use flame arrestors where appropriate▪ Leak test systems and equipment before use.

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Operating procedures and trainingThe operating safety of equipment requires proper training, clear and concise instructionsand regular maintenance. It is important that all personnel who use vacuum equipment areproperly trained, qualified and, where necessary, supervised.

If you are unsure about any detail of operation or safety which relates to Edwardsequipment, please contact us for advice.

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P40040100_E - Operating procedures and training

Summary▪ Perform a hazard assessment to identify and where possible eliminate and if not

mitigate all hazards. This needs to be carried out for vacuum system design,construction, commissioning, operation, maintenance and decommissioning.

▪ Consider all possible chemical reactions within your system. Make allowance forabnormal chemical reactions, including those which could occur under faultconditions.

▪ Refer to material data sheets/Material Safety Data Sheets when you assess thepotential hazards associated with your process materials, for example, auto-ignition.

▪ Use dilution techniques to minimize reactions with oxidants and flammablematerials.

▪ Use the correct type of lubricant in your pump when you pump oxidants andpyrophoric materials.

▪ Do not use heavy metals in the gas path of your pumping system if your processproduces or uses sodium azide.

▪ When you perform safety calculations, ensure that the safe working pressures forall components in the system are taken into account. Ensure that you also takeaccount of abnormal and fault conditions.

▪ Ensure that you incorporate the correct type of pressure relief devices and thatthey are suitably rated for your application.

▪ Ensure that exhaust blockages cannot occur.▪ Ensure that dilution gases are properly regulated and monitored.▪ If you pump hazardous materials, you must design the system to fail to a safe

condition.▪ Use PFPE (perfluoropolyether) oil and lubricants when you pump oxidants.▪ Use an inert gas to dilute flammable and pyrophoric gas to safe levels or ensure

that you stay above the upper flammable / explosion limit considering suitablesafety factors during all process conditions including faults.

▪ You must not allow the maximum pressure of the system to exceed the maximumpressure rating of any single part of the system.

▪ Consider the use of dry pumps in preference to oil sealed pumps where hazardsassociated with oil in the swept volume exist.

▪ Eliminate stagnant volumes.▪ Ensure that the system is suitably controlled and regulated.▪ Use flame arresters where appropriate.▪ Leak test systems and equipment before use.

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P40040100_E - Summary

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Vacuum Pump and Vacuum Systems Safety Manual